A conventional axial flow gas laser oscillator is described hereinafter with reference to drawings. FIG. 10 shows a schematic diagram of the construction of a conventional gas laser oscillator. In FIG. 10, discharge tubes 1 are made of an insulator such as glass and have anodes 2 and cathodes 3 disposed in the interior thereof. High-voltage direct current or HVDC power supplies 4 are connected to the anodes 2 and the cathodes 3, and apply a voltage, for example 30KV, between the anodes 2 and the cathodes 3. Discharge spaces 5 exist within the discharge tubes 1 across the anodes 2 and the cathodes 3. Connecting tubes S are made of an insulator such as glass and a total reflection mirror 6 and a partial reflection mirror 7 are connected to the discharge tubes 1 on the cathodes 3 side via the connecting tubes 8. A laser beam 9 (an arrow) is output from the partial reflection mirror 7. The other arrows 10 indicate the flow direction of the laser gas circulating within the axial flow gas laser oscillator. A blower 11 forces the laser gas to flow in the axial direction of the discharge tubes 1. Heat exchangers 12 cool the laser gas which has been warmed up by an electric discharge in the discharge spaces 5 and the blower 11. The blower 11 effects a flow speed of the gas of approximately 200 m/sec in the discharge spaces 5. A gas outlet pipe 13 made of an insulator exhausts the laser gas from the anodes 2 side of the discharge tubes 1, and forms a part of a circulation route of the laser gas. Gas inlet pipes 14 made of an insulator supplies the laser gas from the cathodes 3 side of the discharge tubes 1, and form a part of the circulation route of the laser gas. The anodes 2 are disposed in the center of a resonator and is applied with a high voltage. The cathodes 3 are disposed, one on each end of the resonator without being grounded, so as to maintain the balance of the discharge current of a plurality of discharge tubes. As a result, the potential of the cathodes 3 is constantly high during operation. Therefore, an electrical insulation distance in a laser gas atmosphere must be maintained between the cathodes 3 and grounded heat exchangers 12 as well as between the cathodes 3 and the total reflection mirror 6 and the partial reflection mirror 7. To secure this, a gas outlet pipe 13 and gas inlet pipes 14, both made of an insulator are disposed between the cathodes 3 and the heat exchangers 12, and connecting tubes 8 also made of an insulator is disposed between the cathodes 3 and total reflection mirror 6 and partial reflection mirror 7.
The construction of the conventional axial flow gas laser oscillator has been described above.
Next, the operation of the conventional axial flow gas laser oscillator is described.
A high voltage is supplied across the anodes 2 and cathodes 3 by the HVDC power supplies 4 to generate a glow-discharge in the discharge spaces 5. The laser gas flowing through the discharge spaces 5 gets excited by gaining this discharge energy. The excited laser gas then is optically resonated by an optical resonator comprising the total reflection mirror 6 and partial reflection mirror 7, and the laser beam 9 is output from the partial reflection mirror 7. The laser beam 9 is used for a wide range of laser beam machining applications.
With the construction described above, if the discharge is continued after impurities have been introduced into the laser gas flowing in the discharge tubes 1 or gas mixing ratio has been changed, the discharge in the discharge tubes 1 becomes unstable, resulting in wide fluctuation of the potential of the cathodes 3. A fluctuation in the potential of the cathodes 3 allows a micro discharge current to flow in the laser gas inside the connecting tubes 8 thereby degrading the total reflection mirror 6 and the partial reflection mirror 7 employed as internal mirrors of the resonator.
The present invention aims at solving the problem mentioned above and to provide a gas laser oscillator which realizes a stable laser beam mode and laser output for a long time.